refactor: modularize cli helpers

src/infra/binaries.ts

@@ -0,0 +1,14 @@
+import { runExec } from "../process/exec.js";
+import { defaultRuntime, type RuntimeEnv } from "../runtime.js";
+
+export async function ensureBinary(
+	name: string,
+	exec: typeof runExec = runExec,
+	runtime: RuntimeEnv = defaultRuntime,
+): Promise<void> {
+	// Abort early if a required CLI tool is missing.
+	await exec("which", [name]).catch(() => {
+		runtime.error(`Missing required binary: ${name}. Please install it.`);
+		runtime.exit(1);
+	});
+}